A new assay for global fibrinolysis capacity (GFC): Investigating a critical system regulating hemostasis and thrombosis and other extravascular functions

For many years, the importance of fibrinolysis has been recognized, first for its intravascular antithrombotic action, and more recently for its many extravascular activities, associated with matrix degradation and tissue remodeling. In the blood circulation system, fibrinolysis prevents thrombosis, and is associated with various biological and clinical situations: risk factors for cardio-vascular diseases in high risk clinical situations (type II diabetes, hypertension, triglycerides, high BMI, elevated glucose, etc.), probably resulting from a significant reduction of the fibrinolysis potential, and elevation of PAI-1. Noteworthy, t-PA is mainly present as an inactive complex with PAI-1, and its concentration in plasma tends to follow that of PAI-1, but in a lesser extent. Hypofibrinolysis can favor the occurrence of thrombotic events, and possibly other biological dysfunctions. Fibrinolysis activity is however difficult to evaluate as it has a delayed activity after clot formation, is initiated and regulated after fibrin generation, and conversely to clotting, its action is delayed (long lag phase) and slow, before being dramatically amplified leading to rapid clot dissolution. We have designed a new assay for evaluating the global fibrinolytic capacity (GFC) in the body. Reagents are used in association with a specific instrument, which can be connected to any computer, and dedicated software is used for analyzing clot lysis kinetics. The assay is performed in a micro-cuvette, introduced into one of the instrument wells at 37 °C, and light transmittance is continuously measured. Assayed plasma is first supplemented with a limited and constant amount of t-PA with silica and is then clotted with thrombin and calcium. Clot dissolution (measurement of turbidity change) is recorded over time using the dedicated instrument (Lysis Timer), and clot lysis kinetics are analyzed with the associated software: primary and secondary derivatives of the light transmission curve give information on kinetics and completion of clot dissolution. Total assay time is about 1 h (but in the presence of hypofibrinolysis it can be prolonged). The concentration of t-PA used for the assay has been adjusted (100 ng/ml) to obtain an optimal sensitivity to hypofibrinolysis within a short time interval, and clot dissolution occurs within about 45 min for normal individuals, with a broad range from 30 min to 60 min, with some samples presenting a clot dissolution time >60 min (hypofibrinolysis). This new assay is performed with the tested plasma intrinsic factors, especially its own fibrinogen, and only exogeneous t-PA is added. GFC is highly sensitive to PAI-1 activity, but other factors regulating fibrinolysis contribute to the clot dissolution kinetics. Freshly prepared or frozen and thawed citrated plasma can be used. The usefulness of this assay for clinical applications is under investigation. Although fibrinolysis is mainly initiated in the body upon stimulation or blood clotting, and rapidly diluted and inhibited in the circulation, evaluation of its "residual" activity in plasma is expected to reflect its global body potential.

Relationship between plasma markers of endothelial cell integrity and the Framingham cardiovascular disease risk-factor scores in apparently healthy individuals

Separate reports have identified differences in plasma levels of the endothelial markers soluble E-selectin, von Willebrand factor (vWf) and soluble thrombomodulin in each of the major modifiable risk factors for atherosclerosis (smoking, hypertension and hypercholesterolaemia), and abnormal levels of some plasma markers predict various adverse cardiovascular events. However, it is unclear whether there is an increasing effect on the endothelium with a worsening risk-factor profile. We measured the three endothelial cell markers by enzyme-linked immunosorbent assay in the plasma of 200 subjects (mean age, 54 years; 58% men) free of the symptoms and clinical signs of atherosclerosis. Levels of the markers were then correlated with the Framingham coronary heart disease (CHD) and cerebrovascular disease (CVD) scores to help determine which (if any) may be useful as good laboratory predictors of future cardiovascular events in prospective epidemiological studies. vWf correlated with CHD (r(s) = 0.269, < 0.001) and CVD risk (r(s) = 0.331, P < 0.001), but soluble E-selectin correlated only with CHD risk (r(s) = 0.163, P = 0.021). We conclude that, of the three specific endothelial markers, vWf correlates most closely with the Framingham risk-factor prediction scores and therefore may be the better plasma endothelial marker of the future development of an atherothrombotic event.

Longitudinal study on activated factors XII and VII levels during normal pregnancy

Levels of activated factor XII (FXIIa) and VII (FVIIa) were determined in 100 women with uneventful pregnancies. Samples were divided into five study intervals: three during pregnancy, one at delivery and one 3 d postpartum. The median (range) for FXIIa levels were 3.4 ng/ml (1.2-9.1) from 11 to 20 weeks, 4.6 ng/ml (1.4-15.2) from 21 to 30 weeks, 5.4 ng/ml (1.9-14.3) from 31st week to delivery, 5.2 (1.3-11.4) at delivery and 4.3 (1.8-8.5) ng/ml in the postpartum sample. For FVIIa the median and range levels for the five periods were 4.9 (1.7-77.3), 7.2 (2.5-80.4), 11.1 (2.9-90.6), 12.0 (3.1-64.1) and 8.2 (4.0-23.5) ng/ml. Although the increase of FVIIa was higher than that of FXIIa during pregnancy, the overall changes of FXIIa and FVIIa were highly correlated (P<0.0001). At each time period the changes of FVIIa correlated with FVII:C which was not the case with FVII:Ag. These data indicate that during pregnancy both the contact phase and extrinsic pathway are activated.